An investigation of the roles of surface aluminum and acid sites in the zeolite MCM-22

Ammonia adsorption studies reveal that the observed Lewis acidity in the zeolite MCM-22 is derived from at least two types of framework aluminum sites (AlF), that is, octahedral AlF and three-coordinate AlF. Comparative ammonia or trimethylphosphine (TMP) adsorption experiments with MCM-22 confirm that octahedral Al species gives rise to the signal at delta(iso) approximately 0 in the 27Al NMR spectrum; this is a superposition of two NMR signals from the different Al species on the water-reconstructed zeolite surface. A sharp resonance assigned to framework Al reversibly transforms on ammonia adsorption to delta(iso)27Al approximately 55 from tetrahedral AlF, while the broad peak is assigned to nonframework aluminum which results from hydrothermal treatment. This study also demonstrates the effectiveness of 27Al magic angle spinning (MAS) and multiple quantum (MQ) MAS NMR spectroscopy as a technique for the study of zeolite reactions.     

铝在MCM-22分子筛骨架上分布的27Al MQ MAS NMR研究

利用二维多量子魔角旋转（2D MQ MAS）技术并结合量子化学计算，研究了铝在MCM-22分子筛骨架上的分布，并对铝的不等价四面体位进行了归属.在27Al 2D 5Q MAS NMR谱中骨架四配位铝的范围内观察到3个信号，证明MCM-22分子筛有3种骨架铝.经计算这3种骨架四配位铝的各向同性化学位移和四极作用常数分别为：δ 50.5、δ 57.3、δ 62.4和1.74、1.68、1.92 MHz. MCM-22分子筛结构中有8种结晶学不等价四面体（T）位.我们通过模拟MCM-22分子筛的27Al 2D 5Q MAS NMR谱，认为8种不等价T位分为3组. T2、T6位上的铝分别与δ 61、δ 49处的信号相关， T1、T3、T4、T5、T7、T8位上的铝对δ 56处的共振峰有贡献.当硅铝原子数比(Si/Al)在10～15之间变化时，铝在MCM-22分子筛的骨架上是无规占据的.     

Multinuclear solid-state high-resolution and 13C -{27Al} double-resonance magic-angle spinning NMR studies on aluminum alkoxides

A combination of 27Al magic-angle spinning (MAS)/multiple quantum (MQ)-MAS, 13C-1H CPMAS, and 13C-{27Al} transfer of population in double-resonance (TRAPDOR) nuclear magnetic resonance (NMR) were used for the structural elucidation of the aluminum alkoxides aluminum ethoxide, aluminum isopropoxide, and aluminum tertiarybutoxide. Aluminum alkoxides exist as oligomers with aluminum in different coordinations. High-resolution 27Al MAS NMR experiments with high-spinning speed distinguished the aluminum atoms in different environments. The 27Al MAS NMR spectrum gave well-resolved powder patterns with different coordinations. Z-filter MQ-MAS was performed to obtain the number and types of aluminum environments in the oligomeric structure. 13C-1H CPMAS chemical shifts resolved the different carbon species (-CH3, =CH2, =CH-, and =C=) in the structures. 13C-{27Al} TRAPDOR experiments were employed to obtain relative Al-C dipolar interactions and to distinguish between terminal and bridging alkoxides in the crystallographic structures. The complete characterization of selected aluminum alkoxides using advanced NMR methods has evidenced the tetrameric structure for aluminum isopropoxide and the dimeric structure for aluminum tertiary-butoxide, as reported in the literature, and proposed a polymeric structure for aluminum ethoxide.     

HZSM-5分子筛焙烧脱铝的27Al MQMAS NMR研究

用29Si、27Al魔角旋转固体核磁共振(MAS NMR)结合二维多量子魔角旋转(2D MQMAS)技术对焙烧脱铝的HZSM-5分子筛中铝的配位状态进行了研究.结果表明,HZSM-5分子筛经焙烧后,在化学位移(δ)45处出现一宽峰信号,其主要来自扭曲四配位铝.通过二维三量子铝谱计算出扭曲四配位铝的四极作用常数约为5.2 MHz.对700和750 ℃焙烧样品的铝谱进行分峰拟合,发现在δ 30处又出现一个小峰,归属为非骨架五配位铝.同时,在750 ℃焙烧样品的二维多量子铝谱中直接观察到非骨架五配位铝的信号.焙烧温度低于700 ℃,脱铝不明显；高于700 ℃,引起分子筛骨架的显著脱铝.焙烧还造成部分骨架铝的信号变得“不可观测”.     

Effects of adsorbate molecules on the quadrupolar interaction of framework aluminum atoms in dehydrated zeolite H,Na-Y

The effect of adsorbate molecules on the quadrupolar interaction of framework aluminum atoms with the electric field gradient in dehydrated zeolite H,Na-Y has been studied by (27)Al MAS NMR and (27)Al MQMAS NMR spectroscopy at magnetic fields of 9.4 and 17.6 T. Upon adsorption of molecules interacting with bridging OH groups by hydrogen bonds (acetonitrile and acetone), the quadrupole coupling constant of framework aluminum atoms was found to decrease from 16.0 MHz (unloaded zeolite) to 9.4 MHz. Adsorption of molecules, which cause a proton transfer from the zeolite framework to the adsorbates (ammonia and pyridine), reduces the quadrupole coupling constant to 3.8 MHz for coverages of 0.5-2 molecules per bridging OH group. The experiments indicate that the quadrupole coupling constant of framework aluminum atoms in dehydrated zeolite H,Na-Y reflects the chemical state of adsorbate complexes formed at bridging OH groups. In agreement with earlier investigations it was found that a proton affinity of the adsorbate molecules of PA = 812-854 kJ/mol is necessary to induce a proton transfer from the zeolite framework to the adsorbed compounds. This proton transfer is accompanied by a strong improvement of the tetrahedral symmetry of zeolitic framework AlO(4) tetrahedra and a decrease of the electric field gradient.     

Methane dehydrogenation and aromatization in the absence of oxygen on Mo/HZSM-5: A study on the interaction between Mo species and HZSM-5 by using Al and Si MAS NMR

By using a high-resolution solid state nuclear magnetic resonance spectrometer with ²⁷Al and ²⁹Si probes, the interaction between Mo species and HZSM-5 of frsol|Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminum in the zeolite can be easily extracted by the introduction of Mo species. The extractability of framework aluminum by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al₂(MoO₄)₃. The dealumination of the catalyst having a Mo loading of 15% and had been calcined at 973 K is so severe that all the aluminum in the framework are extracted and no framework Al could be detected by ²⁷Al MAS NMR. The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The Si/Al ratio measured from ²⁹Si MAS NMR further confirms the dealumination process observed by ²⁷Al MAS NMR. The MAS NMR results give us an evidence that Al₂(MoO₄)₃ crystallites are much less active for the reaction.     

Distribution of aluminum and boron in the periodical building units of boron-containing Beta zeolites

Various boron only ([B]-BEA) as well as aluminum- and boron-containing beta zeolites ([Al,B]-BEA) have been prepared and modified by ion exchange of ammonium, sodium, and nickel ions. The zeolite samples have been characterized by 11B, 27Al, and 29Si MAS as well as three of them by 11B and 27Al 3Q-MAS NMR spectroscopy. The quantitative contributions of defect-free Si(nX) (n = 2, 1, 0; X = Al, B) and Si(OH)x (x = 2, 1) sites to the NMR signal intensities were calculated from the various Si/(Al + B) ratios and relative 11B, 27Al, and 29Si NMR signal intensities using the special distribution of aluminum and boron in different periodical building units of the zeolite framework. The boron atoms are sitting exclusively in diagonal positions in the four-membered rings of [B]-BEA zeolites, while the aluminum atoms are situated both in diagonal and lone positions in the four-membered rings of [Al,B]-BEA zeolites. A higher part of boron atoms are positioned in framework-related deformed tetrahedral boron species than in lattice positions in the [B]-BEA than in the [Al,B]-BEA zeolites. All extraframework octahedral aluminum species are transformed back to lattice positions due to ion exchange from the protonated form to ammonium-, sodium-, or nickel-ions containing zeolites. Oppositely, trigonal boron leaves the zeolite structure completely during ion exchange.     

Characterization of framework and extra-framework aluminum species in non-hydrated zeolites Y by 27Al spin-echo, high-speed MAS, and MQMAS NMR spectroscopy at B0 = 9.4 to 17.6 T

27Al spin-echo, high-speed MAS (nu(rot) = 30 kHz), and MQMAS NMR spectroscopy in magnetic fields of B0 = 9.4, 14.1, and 17.6 T were applied for the study of aluminum species at framework and extra-framework positions in non-hydrated zeolites Y. Non-hydrated gamma-Al2O3 and non-hydrated aluminum-exchanged zeolite Y (Al,Na-Y) and zeolite H,Na-Y were utilized as reference materials. The solid-state 27Al NMR spectra of steamed zeolite deH,Na-Y/81.5 were found to consist of four signals. The broad low-field signal is caused by a superposition of the signals of framework aluminum atoms in the vicinity of bridging hydroxyl protons and framework aluminum atoms compensated in their negative charge by aluminum cations (delta(iso) = 70 +/- 10 ppm, C(QCC) = 15.0 +/- 1.0 MHz). The second signal is due to a superposition of the signals of framework aluminum atoms compensated by sodium cations and tetrahedrally coordinated aluminum atoms in neutral extra-framework aluminum oxide clusters (delta(iso) = 65 +/- 5 ppm, C(QCC) = 8.0 +/- 0.5 MHz). The residual two signals were attributed to aluminum cations (delta(iso) = 35 +/- 5 ppm, C(QCC) = 7.5 +/- 0.5 MHz) and octahedrally coordinated aluminum atoms in neutral extra-framework aluminum oxide clusters (delta(iso) = 10 +/- 5 ppm, C(QCC) = 5.0 +/- 0.5 MHz). By chemical analysis and evaluating the relative solid-state 27Al NMR intensities of the different signals of aluminum species occurring in zeolite deH,Na-Y/81.5 in the non-hydrated state, the aluminum distribution in this material was determined.     

焙烧对HZSM－5分子筛结构的影响

运用魔角自转固态核磁共振谱（ＭＡＳ－ＮＭＲ），研究了焙烧对ＨＺＳＭ－５分子筛结构的影响．结果表明，高温焙烧将引起ＨＺＳＭ－５分子筛骨架的脱铝，当焙烧温度从５００℃增加到７００℃时，ＨＺＳＭ－５的骨架Ｓｉ／Ａｌ比由１６．７增加至２２．７；而当焙烧温度由７００℃到８００℃时，骨架Ｓｉ／Ａｌ比则由２２．７增加到了４８．５．２７Ａｌ－ＭＡＳＮＭＲ结果表明，从骨架上脱下来的铝，部分地形成了ＮＭＲ不可见的无定形态．随着焙烧温度的升高，ＮＭＲ不可见铝增多     

27Al和29Si MAS-NMR对Mo/HZSM-5催化剂的研究

使用＾２９Ａｌ固体离分辨核磁技术对甲烷无氧芳构化催化剂Ｍｏ／ＨＺＳＭ－５分子筛进行了研究，发现ＨＺＳＭ－５分子筛本体中仅含有少量非骨架Ａｌ，Ｍｏ物种与分子筛骨架Ａｌ的相互作用随Ｍｏ担载量以及焙烧的温度的升高而增加，在高温焙烧下，Ｍｏ物种会使分子筛骨架严重脱铝，并且生成Ａｌ２（ＭｏＯ４）３新相，最终导致分子筛骨架塌陷，催化性能下降。     

Solid-state NMR identification and quantification of newly formed aluminosilicate phases in weathered kaolinite systems

The weathering of a specimen kaolinite clay was studied over the course of 369 d via solid-state 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and high-field 27Al MAS NMR. The chosen baseline solution conditions (0.05 mol kg-1 of Al, 2 mol kg-1 of Na+, 1 mol kg-1 of NO3-, 1 mol kg-1 of OH-, and pH approximately 13.8) approximate those of solutions leaking from waste tanks at the Hanford Site in Richland, WA. Nonradioactive Cs and Sr cations were added to this synthetic tank waste leachate (STWL) solution at concentrations of 10(-3), 10(-4), and 10(-5) molal (m) to represent their radionuclide counterparts. The transformations of silicon- and aluminum-containing solid phase species were monitored quantitatively by using NMR spectroscopy, with the resulting spectra directly reporting the influence of the initial Cs and Sr on formation and transformation of the neo-formed solids. At the lowest concentration of Cs and Sr employed (10(-5) m in each cation) peaks consistent with the formation of zeolite-like minerals were detected via 29Si and 27Al MAS NMR as early as 33 d. At concentrations of 10(-3) m in each cation, new silicon species are not detected until 93 d, although neophases containing four-coordinate aluminum were detectable at earlier reaction times via 27Al MAS NMR. At the highest magnetic field strengths employed in this NMR study, deconvolutions of resonances detected in the tetrahedral region of the 27Al MAS spectra yielded multiple components, indicating the existence of at least four new aluminum-containing phases. Two of these phases are identified as sodalite and cancrinite through comparison with diffuse-reflectance infrared (DRIFT) spectra and powder X-ray diffraction (XRD) results, while a third phase may correlate with a previously detected aluminum-rich chabazite phase. All measurable solid reaction products have been quantified via their 27Al MAS resonances acquired at high magnetic field strengths (17.6 T), and the quantitative nature of the 27Al NMR data shows that cancrinite growth increases while sodalite reaches a steady state with respect to total aluminum in the solid phases. The data also relate the coupling of Cs sorption to the ripening of feldspathoid phases in this heterogeneous system as a function of time, and illustrate the important influence of co-contaminants on the environmental reaction kinetics studied here.     

酸处理对斜发沸石结构影响的研究

采用不同浓度硝酸对斜发沸石（HEU）进行改性处理,结合元素分析（ICP-AES）、N₂物理吸附、X射线粉末衍射（XRD）、魔角旋转固体核磁（MAS NMR）等测试手段及DFT理论计算,研究了酸处理对斜发沸石结构的影响。结果表明,硝酸处理对不同平衡阳离子的HEU（Na-K-HEU、NH₄-HEU、H-HEU）具有不同的脱铝效果。酸处理后Na-K-HEU和NH₄-HEU的硅铝比、比表面积均显著升高。随硝酸浓度增大两个沸石样品的脱铝程度逐渐增加,同时骨架结构也逐渐破坏,硝酸浓度达到4 mol/L时其相对结晶度已低于50%。而H-HEU样品的骨架结构稳定,随硝酸浓度的增大铝含量轻微降低,硝酸浓度达到6 mol/L时相对结晶度仍高达94.8%。阳离子反交换实验结果证明,平衡阳离子的类型不是影响HEU骨架稳定性的主要因素。Na-K-HEU和经硝酸铵交换后的NH₄-HEU中铝都以骨架铝的形式存在,而在后者焙烧成为H-HEU时出现部分非骨架铝,伴随了骨架的稳定化过程。     

天然CXN沸石分子筛水热稳定性研究 II. 水蒸汽处理温度对铵型沸石物化性质的影响

在前文研究天然Stilbite沸石(CXN沸石)水热稳定性影响因素的基础上, 以27Al与29Si MAS NMR, NH3-TPD和低温氮吸附等详细研究了铵型CXN沸石骨架铝配位状态和硅配位状态, 表面酸性与孔性质等与水蒸汽处理温度的关系. 随温度升高, 沸石骨架硅铝比逐渐提高, 并伴随硅羟基缺陷增多. 经750 ℃水蒸汽处理3 h后沸石骨架硅铝比可达到21.3. 沸石总酸量随水蒸汽处理温度的提高而降低, 沸石骨架铝脱除造成沸石孔道部分被堵塞, 但同时形成有利于分子扩散的介孔.     

Solid-state NMR detection, characterization, and quantification of the multiple aluminum environments in US-Y catalysts by (27)Al MAS and MQMAS experiments at very high field.

The detection of all of the aluminum present in steamed zeolite H-Y catalysts by (27)Al MAS NMR at 14.4 T (600 MHz for (1)H) and 18.8T (800 MHz for (1)H) is reported. Further, it is shown that it is possible by (27)Al MAS and MQMAS NMR measurements to clearly identify four separate aluminum environments which are characteristic of these materials and to unambiguously assign their coordinations. Average chemical shift and quadrupolar coupling parameters are used to accurately simulate the (27)Al MAS NMR spectra at 9.4 T (400 MHz for (1)H), 14.4 T (600 MHz for (1)H) and 18.8 T (800 MHz for (1)H) in terms of these four aluminum environments. In addition, these average chemical shift and quadrupolar coupling parameters are used to calculate peak positions in the (27)Al MQMAS isotropic dimension that are in good agreement with the experimental data acquired at 9.4 and 18.8 T.     

Synthesis of mesoporous zeolite single crystals with cheap porogens

Mesoporous zeolite (silicalite-1, ZSM-5, TS-1) single crystals have been successfully synthesized by adding soluble starch or sodium carboxymethyl cellulose (CMC) to a conventional zeolite synthesis system. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption analysis, ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS NMR), temperature-programmed desorption of ammonia (NH₃-TPD) and ultraviolet-visible spectroscopy (UV-vis). The SEM images clearly show that all zeolite crystals possess the similar morphology with particle size of about 300 nm, the TEM images reveal that irregular intracrystal pores are randomly distributed in the whole crystal. ²⁷Al MAS NMR spectra indicate that nearly all of the Al atoms are in tetrahedral co-ordination in ZSM-5, UV-vis spectra confirm that nearly all of titanium atoms are incorporated into the framework of TS-1. The catalytic activity of meso-ZSM-5 in acetalization of cyclohexanone and meso-TS-1 in hydroxylation of phenol was also studied. The synthesis method reported in this paper is cost-effective and environmental friendly, can be easily expended to prepare other hierarchical structured zeolites.     

DFT计算结合固体NMR研究富铝SSZ-13的铝分布和Br?nsted酸性

具有菱沸石(CHA)结构的SSZ-13分子筛在甲醇制烯烃(MTO)及柴油机车尾气氨选择性催化还原(NH_3-SCR)反应中具有重要的应用,采用富铝SSZ-13可以调节MTO反应的烯烃选择性和提升NH_3-SCR的低温脱硝活性,因此SSZ-13中的铝含量和分布与对应的酸性决定了其催化性能。本文采用密度泛函理论结合固体核磁共振实验研究了富铝和富硅HSSZ-13的Al位置与Br?nsted酸强度的内在关系。通过计算取代能发现,对于孤立Al位,质子位于Al周围4个不同O位时能量差异较小,最稳定的B酸位点是O(1)―H。对于富铝SSZ-13,两个Al原子位于同一六元环的对位是Al-Si-Si-Al (NNNN)序列中最稳定的结构,而Al-Si-Al (NNN)序列中能量最优的Al分布是两个铝原子排布于六棱柱上下不同的六元环上。通过计算最稳定构型下的质子亲和势、NH3脱附能和吸附氘代乙腈后的1H NMR化学位移,发现富铝SSZ-13中含有Si(2Al)分布的NNN序列导致了其Br?nsted酸强度弱于高硅的分子筛。分峰拟合29Si魔角旋转核磁共振(MASNMR)谱图表明富铝SSZ-13中Si(2Al)的含量在43%以上,而吸附氘代乙腈后的1H MAS NMR实验显示富铝SSZ-13的桥羟基化学位移向低场移动,进一步证明富铝SSZ-13具有较弱的Br?nsted酸强度。     

两步法合成中孔Al-MSU-X

以预先制备的Al-O-Si纳米粒子为前驱物和非离子型表面活性剂聚乙二醇辛基苯基醚(TX-100)为中孔导向剂两步合成了孔道形状为"wormhole-like"的含铝MSU-X介孔材料,并用XRD, HRTEM, N₂吸附-脱附,²⁷Al MAS NMR, NH3-TPD和催化裂化异丙苯对其结构和催化性能进行了表征;结果证明铝原子已被有效地引入了该中孔材料的骨架结构内,从而使得其在异丙苯裂解反应中显示出较高的催化活性.     

H-MCM-22沸石分子筛中Brnsted/Lewis酸协同效应的~1H 和~(27)Al双量子魔角旋转固体核磁共振研究

采用各种固体核磁共振 (NMR) 技术详细研究了 H-MCM-22 分子筛中 Brnsted/Lewis 酸的协同效应. 二维 1H 双量子魔角旋转 (DQ-MAS) NMR 结果表明, 在脱铝 H-MCM-22 分子筛中 Brnsted 酸位 (骨架桥式羟基) 和 Lewis 酸位 (非骨架铝羟基) 之间是空间邻近的, 暗示着可能存在 B/L 酸协同效应. 二维 27Al DQ-MAS NMR 结果揭示了各种铝物种之间的空间邻近性, 表明 B/L 酸协同效应优先发生在 H-MCM-22 分子筛超笼中的骨架 T6 位铝和非骨架铝物种之间. 2-13C-丙酮探针分子实验发现, 因 B/L 酸协同效应而导致脱铝 H-MCM-22 分子筛酸性明显增强, 氘代吡啶探针分子实验也证实在 H-MCM-22 分子筛的超笼中发生了 B/L 酸协同效应. 上述结果将有助于我们理解在脱铝 H-MCM-22 分子筛上发生的多相催化机理.     

丝光沸石水蒸气/酸浸渍脱铝的多核固体核磁共振研究

采用¹H,²⁹Si,²⁷Al魔角旋转固体核磁共振(MASNMR)及¹H-²⁹Si交叉极化(CP)技术研究丝光沸石水蒸气/酸浸渍脱铝过程中各种铝物质的结构与性质.结果表明,丝光沸石上骨架铝原子在水分子作用下,生成非骨架四配位铝物质[Al(OH)₃(H₂O)],分别在²⁷Al谱δ45和¹H谱δ3.0处出现共振信号,这种铝物质不同于扭曲四配位铝,在高温下进一步水合生成Al(OH)₃(H₂O)₂和Al(OH)₃(H₂O)₃,即非骨架五配位和六配位铝物质.¹H-²⁹SiCP和¹H谱证实,水蒸气脱铝使丝光沸石产生了大量的硅羟基和铝羟基.     

^29Si（^27Al）MAS NMR考察镧离子在LaDAlY型沸石中的作用

用~(29)Si(~(27)Al)MAS NMR和辅加乙酰丙酮(acac)处理样品的静态~(27)Al NMR研究了镧离子对脱铝Y型沸石(DAIY)骨架硅、铝和非骨架铝(EFAL)的影响.结果表明,~(29)Si MAS谱的化学位移及其形状不仅取决于连接[SiO_4]四面体的[AlO]-四面体数目,而且还与引入镧离子的量有关.镧离子的引入导致~(27)Al MAS谱的明显宽化和不对称形变.另外,还讨论了镧离子对非骨架铝的影响.